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Blue holes, or underwater sinkholes similar to sink holes on land, are scattered across Florida’s Gulf continental shelf though vary in size, shape and depth, but most are rich in ecological diversity with plants and animals. NOAA-supported project has come out with new findings of one such blue hole called Amberjack Hole.
Last year, in May and September, a team of scientists from Mote Marine Laboratory, Florida Atlantic University/Harbor Branch, Georgia Institute of Technology and the U.S. Geological Society, with support from the NOAA Office of Ocean Exploration and Research, explored one blue hole, dubbed “Amberjack Hole,” approximately 30 miles off west of Sarasota shore.
They deployed divers and a “benthic lander” with scientific instruments collectively weighing more than 270 kilograms (600 pounds into Amberjack Hole, whose bottom extends deeper than 107 meters (350 feet). The team documented life around the rim of the hole and carbon, nutrients, and microscopic life throughout the hole and in its bottom sediments.
The benthic lander was deployed to the bottom of Amberjack Hole to collect data and samples for longer periods than divers can, right where the bottom water meets the sediment. Image courtesy of Mote Marine Laboratory
What Can We Learn?
From this “mission,” scientists are hoping to learn whether these submersed sinkholes are connected to Florida’s groundwater or if there is groundwater intrusion into the Gulf of Mexico. If a particular blue hole is secreting nutrients and thus affecting an area’s primary production or whether such microenvironments harbor unique or new species of microbes. If the Amberjack site should become a protected area or not is the next on agenda.
The rim of Amberjack Hole is 34 meters (113 feet) from the surface, and the rest of the hole extends down another 72+ meters (237 feet)! In May 2019, scientific divers traveled to the bottom of Amberjack Hole and deployed a special benthic lander created for this project to s depth where bottom water meets the sediment.
In September, the team returned with 17 water samples from just outside the hole down to the bottom and collected 4 sediment cores at the bottom. Remarkably, they also discovered two dead but intact smalltooth sawfish, Pristis pectinata, an endangered species, at the bottom of the hole. One of the animals was subsequently recovered to undergo a necropsy.
The deceased sawfish were intact enough to be collected for research, and Mote scientists quickly reported the discovery to NOAA and the Fish and Wildlife Conservation Commission and obtained the required permit for collection of one of the sawfish, a male measuring an impressive 12 feet long. Video courtesy of Mote Marine Laboratory.
A diver’s view looking up to the opening of Amberjack Hole. Image courtesy of Mote Marine Laboratory
Water sampled inside the hole was found to contain naturally occurring isotopes of radium and radon, two markers of groundwater, suggesting that blue holes are not isolated from groundwater and could provide insights into potential groundwater connection between the Floridan Aquifer and the Gulf of Mexico.
Further, in August 2020 and May 2021 a second deeper site, Green Banana, will be explored using the same techniques developed for the Amberjack Hole. The first trip is scheduled for August 2020, and work will continue in 2021.
